The invention relates to an optical waveguide sensor, particularly an optical fiber sensor and more particularly a sensor formed from an optical fiber having a particular unique configuration wherein a suitable indicator is retained within preformed cells in the optical fiber. More particularly, the invention is concerned with a sensor machined out of a single fiber and to a method for the preparation of such sensor.
Optical fiber (or fiber optic) chemical sensors or probes are well known in the art and such sensors normally comprise an optical fiber in association with a suitable indicator for the analyte under investigation. The indicator may be bound to the fiber by chemical or physical means or may be enveloped by a suitable membrane which is permeable to the analyte.
U.S. Pat. No. 4,200,110 discloses a fiber optic probe which includes an ion permeable membrane envelope which encloses the ends of a pair of optical fibers. The probe operates on the technique of optically detecting a change in the color of a pH sensitive dye.
U.S. Reissue Pat. No. 31,879 discloses a method for measuring the concentration of an analyte in a sample which involves measuring a change in the color characteristic of a fluorescent indicator attached to an optical fiber, without or with a gas-permeable membrane.
In each of the above systems the indicator is attached to the end of the fiber optic probe by chemical bonding or with the aid of a diffusion membrane.
It has now been found that certain difficulties previously encountered in the production of an absorption indicator-containing fiber optic sensor can be avoided by retaining the absorption indicator in pre-formed holes in the optical fiber. The same technique also may be used for other types of indicators, for example fluorescent and luminescent indicators.
Furthermore, the technique is applicable to optical waveguides other than optical fibers; for example, integrated optic chips.